Surfaces of many different materials are painted in a variety of applications for aesthetic reasons and for inhibiting corrosion of the surface and a substrate underlying the surface. For a number of reasons, it is desirable to determine thickness of the paint applied to the surface.
It may be desired to apply at least a minimum, predetermined thickness of a paint or primer coating on a surface. Optimal adhesion of a paint coating is a function of thickness. Also, applying at least a minimum, predetermined thickness of paint or primer can ensure that underlying visual features on the surface do not appear through, or “bleed through,” the coating. This is important for projecting a professional image to customers to instill a feeling of confidence, such as through company signage or commercial airline tail art. This is also important for ensuring that a product, such as a motor vehicle or an airplane, displays a finish expected by the customer.
Further, applying at least a predetermined, minimum thickness of paint or primer can also provide a desired amount of protection from corrosion of the underlying surface and substrate. Many surfaces that are painted are subject to environments that are conducive to corrosion. For example, marine vessels operate in water, and often the water is salt water. Motor vehicles and airplanes often operate in rainy or humid environments. Therefore, it is desirable to provide at least a minimum amount of protection against corrosion.
In some applications, weight is a consideration. For example, it is desirable to minimize weight of an airplane to reduce fuel consumption. However, paint and primer can be a significant factor in weight of a product, such as an airplane. Therefore, it may also be desired in some applications to limit thickness of paint or primer coating on a surface to a maximum, predetermined thickness.
In order to ensure that a minimum, predetermined thickness of paint or primer coating is applied and that a maximum, predetermined thickness of paint or primer coating is not exceeded, it would be desirable to nondestructively determine thickness of a paint or primer coating on a surface. However, currently known nondestructive measurement techniques are limited in their applicability.
For example, eddy current testing is currently used to determine paint thickness on metal substrates. As is known, eddy current testing detects electrical currents, known as eddy currents. As a result, eddy current testing can only be used to determine thickness of paint or primer that is coated onto a surface of a metallic substrate.
As a further example, ultrasound testing is used to determine thickness of a paint or primer coating on a surface of a composite or plastic substrate. However, ultrasound testing is not as reliable as eddy current testing. Further, accuracy of ultrasound testing is reduced for coating thicknesses below {fraction (2/1000)} inch (“mils”).
Therefore, there is an unmet need in the art for a simple, reliable, nondestructive method for determining paint thickness regardless of the substrate on which the paint is coated.